Sanjana's Roomie Murder Mystery

As Sanjana entered her house and went to hang her coat, when her roommate yelled, "No, John! Do not attempt it!" There was a shot, and she heard her roommate fall. When she stepped into the kitchen, she saw the girl and the rifle on the ground. A cop, a doctor, and a lawyer were standing nearby. Who murdered Sanjana's roomie, and how did she find out know?

She identified the cop since John was mentioned on his badge. She identified the cop since John was mentioned on his badge.